The 3GPP (3rd Generation Partnership Project) Committee is an organization whose members originate from various regional standardization organizations and particularly the ETSI (European Telecommunication Standardization Institute) for Europe and the ARIB (Association of Radio Industries and Businesses) for Japan, and the purpose of which is to standardize a 3rd generation telecommunication system for mobiles. The CDMA (Code Division Multiple Access) technology has been selected for these systems. One of the fundamental aspects distinguishing 3rd generation systems from 2nd generation systems, apart from the fact that they make more efficient use of the radio spectrum, is that they provide very flexible services. 2nd generation systems offer an optimized radio interface only for some services, for example the GSM (Global System for Mobiles) system is optimized for voice transmission (telephony service). 3rd generation systems have a radio interface adapted to all types of services and service combinations.
Therefore, one of the benefits of 3rd generation mobile radio systems is that they can efficiently multiplex services that do not have the same requirements in terms of Quality of Service (QoS), on the radio interface. In particular, these quality of service differences imply that the channel encoding and channel interleaving should be different for each of the corresponding transport channels used, and that the bit error rates (BER) are different for each transport channel. The bit error rate for a given channel encoding is sufficiently small when the Eb/I ratio, which depends on the coding, is sufficiently high for all coded bits. Eb/I is the ratio between the average energy of each coded bit (Eb) and the average energy of the interference (I), and depends on the encoding. The term symbol is used to denote an information element that can be equal to a finite number of values within an alphabet, for example a symbol may be equivalent to a bit when it can only be one of two values.
The result is that since the various services do not have the same quality of service, they do not have the same requirement in terms of the Eb/I ratio. But yet, in a CDMA type system, the capacity of the system is limited by the level of interference. Thus, an increase in the energy of bits coded for a user (Eb) contributes to increasing interference (I) for other users. Therefore, the Eb/I ratio has to be fixed as accurately as possible for each service in order to limit interference produced by this service. An operation to balance the Eb/I ratio between the different services is then necessary. If this operation is not carried out, the Eb/I ratio would be fixed by the service with the highest requirement, and the result will be that the quality of the other services would be “too good”, which would have a direct impact on the system capacity in terms of the number of users. This causes a problem, since rate matching ratios are defined identically at both ends of the radio link.
This invention relates to a method for configuring a telecommunication system to define rate matching ratios identically at both ends of a CDMA type radio link.
In the ISO's (International Standardization Organization) OSI (Open System Interconnection) model, a telecommunication equipment is modeled by a layered model comprising a stack of protocols in which each layer is a protocol that provides a service to the higher level layer. The 3GPP committee calls the service provided by the level 1 layer to the level 2 layer “transport channels”. A transport channel (TRCH for short) enables the higher level layer to transmit data with a given quality of service. The quality of service is characterized in particular by a processing delay, a bit error rate and an error rate per block. A transport channel may be understood as a data flow at the interface between the level 1 layer and the level 2 layer in the same telecommunication equipment. A transport channel may also be understood as a data flow between the two level 2 layers in a mobile station, and in a telecommunication network entity connected to each other through a radio link. Thus, the level 1 layer uses suitable channel encoding and channel interleaving, in order to satisfy the quality of service requirement.
Solutions proposed by the 3GPP committee to achieve this balancing are illustrated in FIGS. 1 and 2. FIG. 1 is a diagrammatic view illustrating multiplexing of transport channels on the downlink according to the current proposal of the 3GPP committee. In the current proposal of this committee, the symbols processed until the last step 130 described below are bits.
With reference to FIG. 1, a higher level layer 101 periodically supplies transport block sets to the level 1 layer. These sets are supplied in transport channels reference 100. A periodic time interval with which the transport block set is supplied to the transport channel is called the Transmission Time Interval (TTI) of the transport channel. Each transport channel has its own TTI time interval which may be equal to 10, 20, 40 or 80 ms. FIG. 2 shows examples of transport channels A, B, C and D. In this figure, the transport block set received by each transport channel is represented by a bar in the histogram. The length of the bar in the histogram represents a TTI interval of the associated transport channel and its area corresponds to the useful load in the transport block set. With reference to FIG. 2, the duration of the TTI intervals associated with transport channels A, B, C and D is equal to 80 ms, 40 ms, 20 ms and 10 ms respectively. Furthermore, the dotted horizontal lines in the histogram bars indicate the number of transport blocks in each transport block set. In FIG. 2, transport channel A receives a first transport block set A0 comprising three transport blocks during a first transmission time interval, and a second transport block set A1 comprising a single transport block during the next TTI interval. Similarly, transport channel B receives transport block sets B0, B1, B2 and B3 during four consecutive TTI intervals, comprising 0, 2, 1 and 3 transport blocks respectively. Transport channel C receives transport block sets C0 to C7 during eight successive TTI intervals and finally transport channel D receives transport block sets D0 to D15 during sixteen TTI intervals.
Note that a TTI interval for a given transport channel cannot overlap two TTI intervals in another transport channel. This is possible because TTI intervals increase geometrically (10 ms, 20 ms, 40 ms and 80 ms). Note also that two transport channels with the same quality of service necessarily have the same TTI intervals. Furthermore, the term “transport format” is used to describe the information representing the number of transport blocks contained in the transport block set received by a transport channel and the size of each transport block. For a given transport channel, there is a finite set of possible transport formats, one of which is selected at each TTI interval as a function of the needs of higher level layers. In the case of a constant rate transport channel, this set only includes a single element. On the other hand, in the case of a variable rate transport channel, this set comprises several elements and therefore the transport format can vary from one TTI interval to the other when the rate itself varies. In the example shown in FIG. 2, transport channel A has a first transport format for the set A0 received during radio frames 0 to 7, and a second transport format for set A1 during radio frames 8 to 15.
According to the assumptions currently made by the 3GPP committee, there are two types of transport channels, namely real time transport channels and non real time transport channels. No automatic repeat request (ARQ) is used in the case of an error with real time transport channels. The transport block set contains at most one transport block and there is a limited number of possible sizes of this transport block. The expressions “block size” and “number of symbols per block” will be used indifferently in the rest of this description.
For example, the transport formats defined in the following table may be obtained:
Transport formatNumber of transportCorresponding transportindexblocksblock size00—1110021120
In this table, the minimum rate is zero bit per TTI interval. This rate is obtained for transport format 0. The maximum rate is 120 bits per TTI interval and it is obtained for transport format 2.
Automatic repetition can be used in the case of an error with non-real time transport channels. The transport block set contains a variable number of transport blocks of the same size. For example, the transport formats defined in the following table may be obtained:
Transport formatNumber of transportindexblocksTransport block size011601216023160
In this table, the minimum rate is 160 bits per TTI interval. This rate is obtained for transport format 0. The maximum rate is 480 bits per TTI interval and is obtained for transport format 2.
Thus, considering the example shown in FIG. 2, the following description is applicable for transport channels A, B, C and D:
Transport channelATTI interval80 msTransport formatsTransport formatNumber of transportindexblocksTransport block size011601216023160
In FIG. 2, the transport block set A0 is in transport format 2, whereas A1 is in transport format 0.
Transport channelBTTI interval40 msTransport formatsTransport formatNumber of transportindexblocksTransport block size00—128021803380
In FIG. 2, transport block sets B0, B1, B2 and B3 are in transport formats 0, 1, 2 and 3 respectively.
Transport channelCTTI interval20 msTransport formatsTransport formatNumber of transportindexblocksTransport block size00—1110021120
In FIG. 2, transport block sets C0, C1, C2, C3, C4, C5, C6 and C7 are in transport formats 2, 2, 1, 2, 2, 0, 0 and 2 respectively.
Transport channelDTTI interval10 msTransport formatsTransport formatNumber of transportTransport blockindexblockssize00—112022203320
In FIG. 2, transport block sets D0 to D15 are in transport formats 1, 2, 2, 3, 1, 0, 1, 1, 1, 2, 2, 0, 0, 1, 1 and 1 respectively.
For each radio frame, a transport format combination (TFC) can then be formed starting from the current transport formats for each transport channel. With reference to FIG. 2, the transport format combination for frame 0 is ((A,2), (B,0), (C,2), (D,1)). It indicates that transport formats for transport channels A, B, C and D for frame 0 are 2, 0, 2, and 1 respectively. Index 5 is associated with this transport format combination in the following table that illustrates a possible set of transport format combinations to describe the example in FIG. 2:
TransportFrameformat fornumber withCombinationtransport ChannelsthisindexABCDcombination0020011 1020210 2030012 3030113 402218520210602229721105820221 and 29032114 and 15102111411202331221216 and 7
Therefore, with reference once again to FIG. 1, each transport channel reference 100 receives a transport block set at each associated TTI interval originating from a higher level layer 101. Transport channels with the same quality of service are processed by the same processing system 102A, 102B. A frame checking sequence (FCS) is assigned to each of these blocks during a step 104. These sequences are used in reception to detect whether or not the received transport block is correct. The next step, reference 106, consists of multiplexing the various transport channels with the same quality of service (QoS) with each other. Since these transport channels have the same quality of service, they can be coded in the same way. Typically, this multiplexing operation consists of an operation in which transport block sets are concatenated. The next step consists of carrying out a channel encoding operation, 108, on multiplexed sets of blocks. The result at the end of this step is a set of coded transport blocks. A coded block may correspond to several transport blocks. In the same way as a sequence of transport block sets forms a transport channel, a sequence of sets of coded transport blocks is called a coded transport channel. Channels coded in this way are then rate matched in a step 118 and are then interleaved on their associated TTI intervals in a step 120 and are then segmented in a step 122. During the segmentation step 122, the coded transport block sets are segmented such that there is one data segment for each multiplexing frame in a TTI interval in the channel concerned. A multiplexing frame is the smallest time interval for which a demultiplexing operation can be operated in reception. In our case, a multiplexing frame corresponds to a radio frame and lasts for 10 ms.
As already mentioned, the purpose of the rate matching step (118) is to balance the Eb/I ratio on reception between transport channels with different qualities of service. The bit error rate BER on reception depends on this ratio. In a system using the CDMA multiple access technology, the quality of service that can be obtained is greater when this ratio is greater. Therefore, it is understandable that transport channels with different qualities of service do not have the same needs in terms of the Eb/I ratio, and that if the rate is not matched, the quality of some transport channels would be “too” good since it is fixed by the most demanding channel and would unnecessarily cause interference on adjacent transport channels. Therefore, matching the rate also balances the Eb/I ratio. The rate is matched such that N input symbols give N+ΔN output symbols, which multiplies the Eb/I ratio by the
      N    +          Δ      ⁢                          ⁢      N        Nratio. This
      N    +          Δ      ⁢                          ⁢      N        Nratio is equal to the rate matching ratio RF, except for rounding.
In the downlink, the peak/average ratio of the radio frequency power is not very good, since the network transmits to several users at the same time. Signals sent to these users are combined constructively or destructively, thus inducing large variations in the radio frequency power emitted by the network, and therefore a bad peak/average ratio. Therefore, for the downlink it was decided that the Eb/I ratio will be balanced between the various transport channels by rate matching using a semi-static rate matching ratio
      RF    ≈                  N        +                  Δ          ⁢                                          ⁢          N                    N        ,and that multiplexing frames would be padded by dummy symbols, in other words non-transmitted symbols (discontinuous transmission). Dummy symbols are also denoted by the abbreviation DTX (Discontinuous Transmission). Semi-static means that this RP ratio can only be modified by a specific transaction implemented by a protocol from a higher level layer. The number of DTX symbols to be inserted is chosen such that the multiplexing frame padded with DTX symbols completely fills in the Dedicated Physical Data Channel(s) (DPDCH).
This discontinuous transmission degrades the peak/average ratio of the radio frequency power, but this degradation is tolerable considering the simplified construction of the receiving mobile station obtained with a semi-static rate matching ratio.
Referring once again to FIG. 1, the transport channels with different qualities of service after encoding, segmentation, interleaving and rate matching are multiplexed to each other in a step 124 in order to prepare multiplexing frames forming a transport channel composite. This multiplexing is done for each multiplexing frame individually. Since the rate of the multiplexed transport channels may be variable, the composite rate obtained at the end of this step is also variable. The capacity of a physical channel referred to as a DPDCH (Dedicated Physical Data Channel) is limited, consequently it is possible that the number of physical channels necessary to transport this composite may be greater than one. When the required number of physical channels is greater than one, a segmentation step 126 for this composite is included. For example, in the case of two physical channels, this segmentation step 126 may consist of alternately sending one symbol to the first of the two physical channels denoted DPDCH#1, and a symbol to the second physical channel denoted DPDCH#2.
The data segments obtained are then interleaved in a step 128 and are then transmitted on the physical channel in a step 130. This final step 130 consists of modulating the symbols transmitted by spectrum spreading.
DTX symbols are dynamically inserted either for each TTI interval separately in a step 116, or for each multiplexing frame separately in a step 132. The rate matching ratios RFi associated with each transport channel i are determined such as to minimize the number of DTX symbols to be inserted when the total transport channel composite rate after the multiplexing step 124 is maximum. The purpose of this technique is to limit degradation of the peak/average ratio of the radio frequency power in the worst case.
The rate is matched by puncturing (RFi<1, ΔN<0) or by repetition (RFi>1, ΔN>0). Puncturing consists of deleting −ΔN symbols, which is tolerable since they are channel encoded symbols, and therefore despite this operation, when the rate matching ratio RFi is not too low, channel decoding in reception (which is the inverse operation of channel encoding) can reproduce data transported by the transport channels without any error (typically when RFi≧0.8, in other words when not more than 20% of symbols are punctured).
DTX symbols are inserted during one of the two mutually exclusive techniques. They are inserted either in step 116 using the “fixed service positions technique, or in step 132 using the “flexible service positions” technique. Fixed service positions are used since they enable to carry out a blind rate detection with acceptable complexity. Flexible service positions are used when there is no blind rate detection. Note that the DTX symbols insertion step 116 is optional.
During step 116 (fixed service positions), the number of DTX symbols inserted is sufficient so that the data flow rate after this step 116 is constant regardless of the transport format of the transport channels before this step 116. In this way, the transport format of the transport channels may be detected blind with reduced complexity, in other words without transmitting an explicit indication of the current transport format combination on an associated dedicated physical control channel (DPCCH). Blind detection consists of testing all transport formats until the right encoding format is detected, particularly using the frame checking sequence FCS.
If the rate is detected using an explicit indication; the DTX symbols are preferably inserted in step 132 (flexible service positions). This makes it possible to insert a smaller number of DTX symbols when the rates on two composite transport channels are not independent, and particularly in the case in which they are complementary since the two transport channels are then never at their maximum rate simultaneously.
At the present time, the only algorithms that are being defined are the multiplexing, channel encoding, interleaving and rate matching algorithms. A rule needs to be defined to fix a relation in the downlink between the number N of symbols before rate matching and the variation ΔN corresponding to the difference between the number of symbols before rate matching and the number of symbols after rate matching.
Consider the example shown in FIG. 2. Transport channel B accepts four transport formats indexed from 0 to 3. Assume that the coded transport channel originating from transport channel B produces not more than one coded block for each transport format, as shown in the following table.
Transport channelBTTI interval40 msTransport formatsNumber ofTransport formattransportTransportNumber ofCoded blockindexblocksblock sizecoded blockssize (N)00—0—128013682180119233801544
Assume that RFB=1.3333 is the rate matching ratio, then the variation ΔN generated by rate matching varies with each transport format, for example as in the following table:
Transport channelBTTI interval40 msTransport formatsNumber ofTransportcodedCoded blockVariationformat indexblockssize (N)(ΔN)00——11368123211926431544181
Thus, the existence of this type of rule to calculate the variation AN as a function of the number N of symbols before rate matching could simplify negotiation of the connection. Thus, according to the example in the above table, instead of providing three possible variations ΔN, it would be sufficient to supply a restricted number of parameters to the other end of the link that could be used to calculate them. An additional advantage is that the quantity of information to be supplied when adding, releasing or modifying the rate matching of a transport channel, is very small since parameters related to other transport channels remain unchanged.
A calculation rule was already proposed during meeting No. 6 of the work sub-group WG1 of sub-group 3GPP/TSG/RAN of the 3GPP committee in July 1999 in Espoo (Finland). This rule is described in section 4.2.6.2 of the proposed text presented in document 3GPP/TSG/RAN/WG1/TSGR1#6(99)997 “Text Proposal for rate matching signaling”. However, it introduces a number of problems as we will demonstrate. Note the notation used in this presentation is not exactly the same as the notation in document TSGR1#6(99)997 mentioned above.
In order to clarify the presentation, we will start by describing the notation used in the rest of the description.
Let i denote the index representing the successive values 1, 2, . . . , T of the coded transport channels, then the set of indexes of the transport formats of the coded transport channel i are denoted TFS(i), for all values of i ε {1, . . . , T}. If j is the index of a transport format of a coded transport channel i, in other words j ε TFS(i), the set of indexes of coded blocks originating from the coded transport channel i for transport format j is denoted CBS(i, j). Each coded block index is assigned uniquely to a coded block, for all transport formats and all coded transport channels. In summary we have:
  {                                                                                          ∀                                      i                    ∈                                          {                                              1                        ,                        …                        ⁢                                                                                                  ,                        T                                            }                                                                                                                                            ∀                                      j                    ∈                                          TFS                      ⁡                                              (                        i                        )                                                                                                                                                                  ∀                                                            i                      ′                                        ∈                                          {                                              1                        ,                        …                        ⁢                                                                                                  ,                        T                                            }                                                                                                                                            ∀                                                            j                      ′                                        ∈                                          TFS                      ⁡                                              (                                                  i                          ′                                                )                                                                                                                          ⁢                      (                          i              ,              j                        )                          ≠                  (                                    i              ′                        ,                          j              ′                                )                    ⇒                        CBS          ⁡                      (                          i              ,              j                        )                          ⋂                  CBS          ⁡                      (                                          i                ′                            ,                              j                ′                                      )                                =          Ø      ⁡              (        1        )            
where Ø is an empty set. Note that for the purposes of this presentation, the index of a coded block does not depend on the data contained in this block, but it identifies the coded transport channel that produced this coded block, the transport format of this channel, and the block itself if this transport channel produces several coded blocks for this transport format. This block index is also called the coded block type. Typically, coded transport channel i does not produce more than 1 coded block for a given transport format j, and therefore CBS(i,j) is either an empty set or a singleton. If a coded transport channel i produces n coded blocks for transport format j, then CBS(i,j) comprises n elements.
We will also use TFCS to denote the set of transport format combinations. Each element in this set may be bi-univocally represented by a list of (i, j) pairs associating each coded transport channel indexed i in {1, . . . , T} with a transport format with index j in this coded transport channel (jεTFS(i)). In other words, a transport format combination can determine a transport format j corresponding to each coded transport channel i. In the rest of this presentation, it is assumed that the set TFCS comprises C elements, the transport format combinations for this set then being indexed from 1 to C. If 1 is the index of a transport format combination, then the transport format index corresponding to the coded transport channel indexed i in the transport format combination with index 1 will be denoted TFi(1). In other words, the transport format combination with index 1 is represented by the following list:((1, TF1(1)), (2, TF2(1)), . . . , (T, TFT(1)))
The set of block size indexes for any transport format combination 1 is denoted MSB(1). Therefore, we have:
                              ∀                      1            ∈                                          {                                  1                  ,                  …                  ⁢                                                                          ,                  C                                }                            ⁢                              MSB                ⁡                                  (                  1                  )                                                                    =                              ⋃                                                          ≤                                            ≤              T                                ⁢                      CBS            ⁡                          (                              i                ,                                                      TF                    i                                    ⁡                                      (                    1                    )                                                              )                                                          (        2        )            
Furthermore, the number of multiplexing frames in each transmission time interval on the coded transport channel i is denoted Fi. Thus, in the sending system shown in FIG. 1, any block originating from the coded transport channel i is segmented into Fi blocks or segments. Based on the current assumptions made by the 3GPP committee, the sizes of these blocks are approximately equal. For example, if Fi=4 and the block on which segmentation step 122 is applied comprises 100 symbols, then the segments obtained at the end of this step 122 comprise 25 symbols. On the other hand, if the segmented block comprises only 99 symbols, since 99 is not a multiple of 4, then after segmentation there will be either 3 blocks of 25 symbols with 1 block of 24 symbols, or 4 blocks of 25 symbols with a padding symbol being added during the segmentation step 122. However, if X is the number of symbols in the block before segmentation step 122, it can be written that
  ⌈      X          F      i        ⌉is the maximum number of symbols per segment, the notation ┌x┐ denoting the smallest integer greater than or equal to x.
Finally, for a coded block with type or index k, the number of symbols in this coded block before rate matching is denoted Nk, and the variation between the number of symbols after rate matching and the number of symbols before rate matching is denoted ΔNk. Furthermore, note that in the rest of this text, the expressions “rate” and “number of symbols per multiplexing frame” are used indifferently. For a multiplexing frame with a given duration, the number of symbols expresses a rate as a number of symbols per multiplexing frame interval.
Now that the notation has been defined, we can describe the calculation rule described in document 3GPP/TSG/RAN/WG1/TSGR1#6(99)997 “Text proposal for rate matching signaling”.
A prerequisite for this rule is to determine a transport format combination 10 for which the composite rate is maximum. For this transport format combination 10, the variations ΔNkMF for blocks with NkMF symbols before rate matching will be determined. This is done only for transport format combination 10, in other words only for all values k ε MBS(10). The upper index MF in the ΔNkMF and NkMF notations means that these parameters are calculated for a multiplexing frame and not for a TTI interval. By definition:
                    {                                                            ∀                                  i                  ∈                                      {                                          1                      ,                      …                      ⁢                                                                                          ,                      T                                        }                                                                                                                                                                                              ∀                                  j                  ∈                                      TFS                    ⁡                                          (                      i                      )                                                                                                                                            N                  k                  MF                                =                                  ⌈                                                            N                      k                                                              F                      i                                                        ⌉                                                                                                        ∀                                  k                  ∈                                      CBS                    ⁡                                          (                                              i                        ,                        j                                            )                                                                                                                                                                                                  (        3        )            
The next step is to proceed as if the rate matching 118 was carried out after segmentation per multiplexing frame step 122 to define the variations ΔNkMF. For flexible service positions, the variations ΔNkMF for k ∉MBS(10) are calculated using the following equation:
                    {                                                            ∀                                  l                  ∈                                      {                                          1                      ,                      …                      ⁢                                                                                          ,                      C                                        }                                                                                                                        Δ                  ⁢                                                                          ⁢                                      N                    k                    MF                                                  =                                  ⌊                                                                                    Δ                        ⁢                                                                                                  ⁢                                                  N                                                      K                            ⁡                                                          (                              k                              )                                                                                MF                                                                                            N                                                  K                          ⁡                                                      (                            k                            )                                                                          MF                                                              ·                                          N                      k                      MF                                                        ⌋                                                                                                        ∀                                  k                  ∈                                                            MSB                      ⁡                                              (                        1                        )                                                              ⁢                                                                                  ⁢                    and                    ⁢                                                                                  ⁢                    k                                    ∉                                      MSB                    ⁡                                          (                                              1                        0                                            )                                                                                                                                                                                                  (        4        )            where, for any coded block with index k, K(k) is the element of MSB(10) such that coded blocks with index k and K(k) originate from the same coded transport channel and where └x┘ denotes the largest integer less than or equal to x.
For fixed service positions, the variations ΔNkMF for k ∉MSB(10) are calculated using the following equation:
                    {                                                            ∀                                  l                  ∈                                      {                                          1                      ,                      …                      ⁢                                                                                          ,                      C                                        }                                                                                                                        Δ                  ⁢                                                                          ⁢                                      N                    k                    MF                                                  =                                  Δ                  ⁢                                                                          ⁢                                      N                                          K                      ⁡                                              (                        k                        )                                                              MF                                                                                                                          ∀                                  k                  ∈                                                            MSB                      ⁡                                              (                        1                        )                                                              ⁢                                                                                  ⁢                    and                    ⁢                                                                                  ⁢                    k                                    ∉                                      MSB                    ⁡                                          (                                              1                        0                                            )                                                                                                                                                                                                  (                  4          ⁢          bis                )            
Note that the definition of K(k) does not create any problem with this method since, for any value of (i,j), CBS(i,j) comprises a single element and therefore if i is the index of the coded transport channel that produces the coded block with indexed size k, then K(k) is defined as being the single element of CBS(i,10).
With this rule, it is guaranteed that CBS(i,j) is a singleton since, firstly the number of coded blocks per TTI interval is not more than one (basic assumption), and secondly when this number is zero it is considered that the block size is zero and CBS(i,j) then contains a single element k with Nk=0.
Finally, the set of variations ΔNk is calculated using the following equation:
  {                              ∀                      i            ∈                          {                              1                ,                …                ⁢                                                                  ,                T                            }                                                                                                          ∀                      j            ∈                          TFS              ⁡                              (                i                )                                                                                      Δ            ⁢                                                  ⁢                          N              k                                =                                                    F                i                            ·              Δ                        ⁢                                                  ⁢                          N              k              MF                                                                    ∀                      k            ∈                          CBS              ⁡                              (                                  i                  ,                  j                                )                                                                                                 
which, in terms of variation, corresponds to the inverse operation of equation (3), by reducing the considered multiplexing frame period to a TTI interval.
The following problems arise with this calculation rule:
1) nothing is written to say what is meant by the composite rate (the exact rate can only be determined when the variations ΔN have been calculated; therefore, it cannot be used in the calculation rule);
2) even if this concept were defined, it is probable that there are some cases in which the transport format combination that gives the maximum composite rate is not unique; the result is that the definition of the combination 10 is incomplete;
3) equation (4) introduces a major problem. The transport format combination for which the composite rate is maximum is not necessarily such that all transport channels are simultaneously at their maximum rates. In the following, the number of symbols available per multiplexing frame for the CCTrCH composite will be called the maximum physical rate Ndata. The maximum physical rate depends on the resources in allocated physical channels DPDCH. Therefore, it is possible that the maximum physical rate Ndata of the physical channel(s) carrying the composite is insufficient for all transport channels to be at their maximum respective rates simultaneously. Therefore in this case, there is no transport format combination in which all transport channels are at their maximum rates simultaneously. Thus, transport channel rates are not independent of each other. Some transport channels have a lower priority than others such that when the maximum physical rate Ndata is insufficient, only the highest priority transport channels are able to transmit, and transmission for the others is delayed. Typically, this type of arbitration is carried out in the medium access control (MAC) sub-level of the level 2 layer in the OSI model. Since transport channels are not necessarily at their maximum rates simultaneously when the composite is at its maximum rate in transport format combination 1o, in particular it is possible that one of them is at zero rate; therefore, it is possible to find a value k0 ε MBS (10) such that Nk0MF=0, and consequently ΔNk0MF b=0. If k1 ∉MBS(10) is such that k0=K(k1), equation (4) then becomes as follows for k=k1:
      Δ    ⁢                  ⁢          N              k        1            MF        =            ⌊                                    Δ            ⁢                                                  ⁢                          N                              k                0                            MF                                            N                          k              0                        MF                          ·                  N                      k            1                    MF                    ⌋        =          ⌊                        0          0                ·                  N                      k            1                    MF                    ⌋      
It then includes a 0/0 type of indeterminate value. In the same way, it is possible that Nk0MF is very small compared with Nk1MF, even if it is not 0. Thus, whereas the composite is in the transport format combination 10 at its maximum rate, the transport channel corresponding to coded block indexes k0 and k1 is at a very low rate Nk0MF compared with another possible rate Nk1MF for the same transport channel. The result is that equation (4) giving ΔNk1MF as a function of ΔNk0MF amplifies the rounding error made during determination of ΔNk0MF by a factor
      N          k      1        MF        N          k      0        MF  which is very large compared with one. However, such amplification of the rounding error in this way is not desirable.
One purpose of the invention is to suggest a rule for overcoming the disadvantages described above.
Another purpose of the invention is to provide this type of method that can define rate matching for the downlink for all possible situations, and particularly for at least one of the following cases:                when ΔNk0MF and Nk0MF are zero simultaneously;        the        
      N          k      1        MF        N          k      0        MF                   ratio is very large compared with 1;        the rate of at least some transport channels of a transport channel composite depends on at least some other transport channels in the same transport channel composite.        